A facsimile is used to promptly forward an image of graphic material to a remote point. The image of the original material is changed to signal waves and is sent from the dispatching side of the facsimile to a facsimile receiver. The signal waves are changed to an image of the original material in the receiving side of the facsimile.
An optical reader is used to change the image of the original material to signal waves. In the conventional optical reader, the light source for lighting the original material comprises arrays of green light-emitting diodes (LEDs) having a center wavelength of 555 nm so that sufficient contrast of the original material can be obtained so as to clearly distinguish material in red. However, the luminous intensity of a green LED is weak. The length of one LED array and the number of LEDs contained therein correspond to the width of the original material. Two LED arrays are necessary in order to light the original material with a luminous intensity sufficient for the photosensor to recognize the original material. In addition, a high input current fed to the light source is necessary to enhance illumination of the original material. Therefore, excessive heat is generated in the LED arrays and the photosensor is heated, and, as a result, the sensing ability of the sensor is degraded due to an increase in the resistance-in-light of the photosensor and drift of the output voltage thereof.